Irrigation

Planning an Olive Irrigation System
The importance of irrigating Olives

There are many myths about olives circulating amongst first-time growers and enthusiasts as people rush to get into another growing agricultural industry. One of the classic bits of misinformation that inevitably arises is that the “olive tree will grow anywhere and does not need irrigation”. Without pondering all the possible meanings of this statement international experience would say that if you want to develop an economically viable, commercial olive oil plantation you have to irrigate your trees.

It is also abundantly clear from overseas experience that the investment you make in your irrigation system is probably the most important decision you need to make about your olive development. The reason for this is that the irrigation system is not a “necessary evil” but rather an essential management tool that you will need to properly produce consistent quantity and quality of oil.

A review of international research concerning the irrigation of olives reveals a wealth of valuable information. Samish and Spigel (1961) found that oil yield increased as a result of irrigation averaging 30% above that of non-irrigated fruit. Tombesi et al. (1996) found that irrigated trees bear more fruit per tree and produce more oil per hectare than non-irrigated trees. Lavee and Wodner (1991) found that there was a definite relationship between irrigation application and oil accumulation in olives. They also found that irrigation could be used to minimize environmental factors affecting oil production and that well-managed irrigation systems could bring fruit uniformly to maximum oil content and hence provide an economical harvest time.

It is generally accepted that an irrigation system in the correct climatic zone can effectively be used to control bloom, and fruit set and reduce the effect of alternate bearing on oil yield. Table 1 below summarizes the critical stages of growth in the olive tree and points out the effect of low soil moisture levels. It can be seen from examining this information that an irrigation system is a management tool that can have a large bearing on the successful establishment and management of an olive grove.

The olive tree is an alternate-bearing tree, which means that one year it has a heavy crop and in the alternate year it bears a lighter crop. The alternate bearing of the olive tree is caused because the heavy crop suppresses shoot growth and exhausts food reserves. This results in reduced flowering and fruit set in the following year (Sibbett 1994). It has been shown that irrigation applications during the year can overcome the effects of alternate bearing. Irrigation applied early in the growing season enhances shoot growth, which in turn increases the number of fruits in the subsequent season (Samish and Spiegel 1961). The oil percentage at corresponding stages of maturity remained the same and therefore the total oil yield was increased because of the greater number of fruits. Research by Tombesi et al. (1996) found that the number of fruits per tree is determined in spring and early summer. It is in this period that irrigation is essential if a high number of fruits with high oil yield is to be achieved in the subsequent season. Early irrigation is advantageous in overcoming the effects of alternate bearing but has little influence on the current season’s fruit.

Late irrigation (after the spring flush) can be used to manage the current season’s crop by increasing the fruit size and the flesh stone ratio whilst delaying maturation (Samish and Spiegel 1961). The amount of irrigation required is a function of the environmental and soil factors that are peculiar to individual sites. A summary of the importance of irrigation at various times in the season could be stated as follows. Early irrigation encourages shoot growth, which increases the number of fruits in the second season. Irrigation during the season influences fruit size and the stone-flesh ratio.

Table 1 above
Critical periods for soil moisture in olive groves in the southern hemisphere (adapted from Beede and Goldhammer 1994). After reviewing only a small amount of international research it would appear that the need to properly plan and implement irrigation for olive production is quite clear. The quality and performance of the irrigation system will be a major asset in crop management and economically viable production, particularly in areas of low to medium summer rainfall. Now that the need for good irrigation practices has been established it is important to overview the options for irrigation systems and the individual components that make a system functional.

Components of an irrigation system

When discussing irrigation in this context we will confine the discussion to the area of “Micro” irrigation or irrigation using micro-sprinklers and drippers. The use of flood irrigation, travelling irrigates and the like are not considered to be viable irrigation techniques. The main reason for limiting the discussion to micro irrigation is that water resources are extremely limited and it is widely accepted that water availability will continue to decrease and the cost of water will continue to increase. Micro irrigation is the most efficient and ergonomically advantageous to the olive grower, hence the focus of this paper.

The following is a brief description and comment about the most common major components that are found in an irrigation system. The list is not exhaustive and there may be some other items that may specifically suit a particular site and application.

Mini sprinklers

A lot of different mini sprinklers are being used in South Africa. One of the most common methods these days is to use 32 litres per hour static 2700 mini sprinkler on each side of the tree. However, a lot of orchards have been established with swivels wetting a 3-metre radius. The advantages and disadvantages of sprinklers generally are as follows:

Advantages

Operation is easily seen
Two-stage swivel suits developing tree

Disadvantages

Promotes weed growth
Spray is subject to wind drift
Hinders mechanical harvesting
Hinders maintenance of inter-row cover crop
Subject to insect attack
Lateral line can move and pull over the sprinkler
If the emitter blocks the tree doesn’t get watered
Can’t frigate if the wind is blowing
Only 70 – 80 % efficient in water use
Installation is labour intensive
Must punch a hole in lateral accurately
Lateral can be crushed by roots if buried in the first year

Drippers

Inline drip irrigation is by far the most popular form of irrigation in olive groves around the world. With the modern technology available today drip irrigation offers efficient trouble-free irrigation. The factory-extruded drip lines are available in various spacings and flow rates to suit the requirements of individual plantings.

Advantages

Ease of installation.
Excellent water efficiency (85 – 95 %)
Great for establishment
Minimize weed development
Can fertigate at any time
Can move the drip line as the tree develops
Can remove “Oliveline plugs’ as the tree develops
Can inject the dripline subsurface
No damage to the system during harvesting
Can slash the inter-row cover crop when subsurface
Maximum water control
Maximum root development possible

Disadvantages

This May concern some first-time growers
Water is not easily seen when the system is subsurface

Why netafim drippers are so successful?

Netafim can supply you with high-quality, clogging-resistant and reliable drip irrigation equipment. The technology is available for the olive industry and it offers trouble-free operation that is required to make irrigation a tool for management, not a source of headaches. The drippers have gone through many changes since the early days and the improvements and R&D are ongoing.

What you need to do to successfully plan and purchase an Olive irrigation system?

Site Information
The information about your property that you will need to gather to ensure a well-planned irrigation system is as follows:

Soil survey
Have an understanding of the type and variation of soil on your property so that correct irrigation can be designed and varietal allocation can be made.

Water analysis
Take a water sample in a clean plastic 1-litre bottle, fill the bottle to the top, screw the lid on tightly and take it to a laboratory for analysis as soon as possible. Ask the lab to test the pH, and the major ions such as calcium, sodium, chlorine, and also the presence of Iron etc. Iron can be a major problem contributing to blockages, and needs special attention. Contact Netafim’s agricultural department for further advice.

Contact Professionals
Contact professional organizations/individuals or your nearest dealer for further information. There is no need to “reinvent the wheel”, and help is at hand. Ask the people concerned to show a portfolio of successful projects to date, and a proven track record of their performance.

References

Beede, R.H., and Goldhamer, D.A, (1994). Olive Irrigation Management. In ‘Olive Production Manual’ (Eds. Ferguson, L., Sibbett, G.S., and Martin, G.C) the University of California, Division of Agriculture and Natural Resources, Oakland, CA. Publications 3353.

Lavee, S., and Wodner, M. (1991). Factors affecting the nature of oil accumulation in the fruit of olive (Olea Europea L.) cultivars. Journal of Horticultural Science (1991) 66(5): 583-591.

Samish, R.M. and Spiegel, P (1961). The use of irrigation in growing olives for oil production. Israel Journal of Agric, Research. 11:87-95.

Spiegel, P. (1955). The water requirements of the olive tree, critical periods of moisture stress and the effect of irrigation on the oil content of the fruit. 14th International Horticultural Congress, Netherlands, 2, 1363-72.

Tombesi, A., Michelakis, N., and Pastor, M. (1996). Recommendations of the working group on olive farming production techniques and productivity. Olivae 61: 38-51.

Acknowledgement

Netafim Agricultural Services.

For more information and help with your irrigation system contact:
Chris Malan
EMAIL: chrism@netafim.net

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